Cold Plasma Reactor Research Articles

Comparative Study on the Decomposition of Chloroform in Thermal and Cold Plasma

Decomposition of trichloromethane (chloroform, CHCl3) has been studied in inductively coupled RF thermal plasma and in cold plasma, i.e. in silent electric discharge, in neutral and oxidative conditions, as well. GC--MS analysis of the gaseous products and the extracts of the soots were performed and resulted in the formation of solid soot, aliphatic dienes, cyclo-dienes and some aromatic compounds in neutral conditions of RF thermal plasma. In oxidative conditions, however, much less soot and dienes, and much more oxygen-containing products were formed as compared to neutral ones. In the cold plasma reactor, wide range of chlorinated ethane, ethene and propene derivatives were formed in neutral conditions. In oxidative conditions, formation of carbonyl compounds and carbon monoxide as intermediates took place, while the final product consisted of CO2, H2O and Cl2 in the low temperature plasma reactor.

Chemical Vapor Deposition of YBa2Cu3Ox in a Cold Plasma Reactor sing an Aerosol Vaporization Technique

A plasma-enhanced chemical vapor deposition technique, utilizing an aerosol decomposition/vaporization process in a cold plasma reactor, was used to form YBa 2 Cu 3 O x (YBCO) thin films on single-crystal MgO substrates. Aerosol droplets of the precursors were generated by an ultrasonic nebulizer operating at 1.63 MHz, while a 50 kW rf generator, operating at 2.87 MHz, was used to create the plasma and heat a stainless steel susceptor. Nitrate, acetylacetonate, and tetramethylheptanedionate compounds were used as precursors, and distilled water, ethyl alcohol, and an aqueous benzoic acid solution were investigated as solvents for the aerosol solution. The effects of the solubility and decomposition temperature of the chemical precursors, and the vapor pressure of the solvents, on the microstructure and phase assemblage of the deposits were determined. Specific combinations of substrate temperature, in the range of 800°-940°C, and oxygen partial pressure, in the range of 0.3-2.7 kPa, were found to produce in situ, crystalline, stoichiometric YBCO films.

Polystyrene thin films treatment under DC point-to-plane low-pressure discharge in nitrogen for improving wettability

An effort for better understanding of main parameters influence to polystyrene thin films treatment under DC point-to-plane low-pressure discharge in nitrogen is attempted. Voltage-current curves and discharge repetitive current impulses for various gap lengths and gas pressures, in absence and in presence of polystyrene thin films in the cold plasma reactor, evidence that in any case a normal glow discharge regime is established. Atactic polystyrene thin films underlie treatment under the above regime and hydrophilic surfaces are obtained. Wettability is characterized, under certain experimental protocols, by contact angle measurements along the films treated for various gap lengths (d = 0.5, 1, 2 cm), gas pressures (p = 2-10 mbar), gas flow rates (Q = 1-1110$ sccm) and times (ttr = 0-600 s). The best treatment takes place opposite to the point electrode, in an area around the discharge symmetry axis, proving non-homogeneous surface treatment. Atomic Force Microscopy (AFM) shows that this fact does not relate to surface morphological changes. The experimental results confirm that the above treatment yields polystyrene films with very good wettability (typical contact angles: 5-15°) avoiding any obvious material degradation. Ageing effects are introduced but the final wettability in comparison to that before the treatment is increased. The role of excited neutrals and reactive particles with long radiative lifetime (metastables states) is emphasized and seems to lead to polymer treatment through diffusion mechanisms.

Influence of a DC, point-to-plane, low-pressure discharge in nitrogen on polystyrene thin films

In the first part of this work the regime of the DC electrical discharge in nitrogen, in absence and in presence of polystyrene thin films in the cold plasma reactor, for a constant gap length d = 1 cm and for variable pressures (1 mbar < p < 10 mbar) is characterized, while the gas flow rate is maintained at Q = 1 seem. V-I curves underline that in any case a normal glow-like discharge is established. Experimental results bring out that the presence of the films in the volume of the produced plasma seems to modify the structure and some of the discharge characteristics, like the cathode secondary emission effects. V-I curves (I < 200 μA), discharge repetitive current impulses, discharge repetitive emitted light impulses along the discharge symmetry axis and photos of the discharge, in presence and in absence of the films, are presented. In the second part of this paper results of polystyrene thin films treatment under the above DC normal glow-like discharge regime in nitrogen for improving the wettability of the films are presented. The effect of discharge main parameters (pressure p and mean current I through the discharge) on the treatment is studied under certain experimental conditions. The wettability is characterized by contact angle measurements using deionized water drops and the evolution versus the treatment time t tr of the Δθ/θ i = (θi - θf)/θi ratio (θi: the contact angle before the treatment and θf: the contact angle after the treatment) is estimated. It is deduced that optimizing main parameters of the DC electrical discharge in nitrogen it is possible to obtain films with very good wettability (suggestively Δθ/θi = 0.951 corresponding to θ f = 4°, at p = 4 mbar, I = 200 μA, t tr ≅ 600 s). A rapid change of the films surface nature (0 s < t tr < 60 s, suggestively) seems to be followed by a slower one and finally by a saturation. The gas pressure and the discharge mean current seem to play a very important role for the treatment. The experimental results allow us to start a discussion about the possible role of some active particles produced in the plasma to the treatment of the films and especially the role of the neutrals and the metastables.

Difference in Conversions Between Dimethyl Sulfide and Methanethiol in a Cold Plasma Environment

This study compared the conversion of two malodorous substances, dimethyl sulfide (CH3SCH3, DMS) and methanethiol (CH3SH) in a cold plasma reactor. The DMS and CH3SH were successfully destroyed at room temperature. DMS decomposed less than CH3SH at the same conditions. In oxygen-free condition, CS2 and hydrocarbons were the major products, while SO2 and COx were main compounds in oxygen-rich environments. The DMS/Ar plasma yielded more hydrocarbons and less CS2 than that of CH3SH/Ar plasma. In the CH3SH/O2/Ar plasma, rapid formation of SO and CO resulted in the yields much more amounts of SO2 and CO2 than those in the DMS/O2/Ar plasma; and remained only a trace of total hydrocarbons, CH2O, CH3OH, CS2, and OCS. The major differences between the reaction mechanisms of DMS and CH3SH were also proposed and discussed.

Development of Cathode Materials by Plasma Process at Room Temperature

Deposits of La 1-x Sr x MnO 3±δ used as cathode materials in solid oxide fuel cells are obtained by oxidation of nitrate precursors in a cold temperature plasma reactor equipped with a convergent nozzle. Infrared analysis of deposits permitted us to measure the role of plasma parameters on the conversion rate of nitrate precursors. Oxygen and hydroxyl radicals produced by plasma are found to be the major reactive species that lead to the transformation of nitrate precursors into perovskites in this process. Impedance measurements showed the role of plasma parameters on the electrical conductivity of deposits.

Increasing the wettability of EVA trough a laboratory glow discharge cold plasma reactor treatment

Increasing the wettability of EVA trough a laboratory glow discharge cold plasma reactor treatment

Formation of Solid Sulfur by Decomposition of Carbon Disulfide in the Oxygen-Lean Cold Plasma Environment

In general, the conventional thermal processes for treating toxic carbon disulfide (CS2) gas were by the oxidation of sulfur on CS2 to form SO2. However, this study demonstrated that by using a radio-frequency cold plasma reactor in the oxygen-lean condition (O2/CS2 = R = 0.6) at the applied power of 90 W, the decomposition fraction of CS2 could reach 88.2%, and there was 76.9% of input sulfur mass from CS2 converted into solid sulfur with the purity of 99.2%. No solid sulfur was observed for the no-oxygen (R = 0) or oxygen-rich conditions (R = 3.0). Hence, the results of this study provided an approach for sulfur recovery to reduce the emissions of both CS2 and SO2. In addition, the reaction mechanisms for the decomposition of CS2 and for the formation of gaseous SO2, CO, CO2, and OCS in the CS2/O2/Ar plasma were also built up and discussed.

Catalyst Enhanced Oxidation of VOCs and Methane in Cold-Plasma Reactors

Volatile organic compounds, VOCs, are used in a number of industrial processes in a variety of roles, for instance as solvents, cleaners and liquid fuels. During these processes, some of the VOCs, which are known to be air toxins, inevitably escape into the surrounding air. It is the release of this VOC-laden air into the atmosphere that is partly responsible for stratospheric ozone depletion, tropospheric ozone increase, global warming (the Greenhouse Effect) and some health problems. Here, we briefly review some applications of platinum metals catalysts in the abatement of VOCs and in the conversion of methane using cold-plasma techniques. Some information on the abatement of acid gases, the generation and application of non-thermal plasmas is also presented.

Mechanical strength of cold plasma treated PET fibers

In this work, the effects of cold plasma treatment on the mechanical strength of polyethyleneterephthalate (PET) fibers has been verified. Single fibers were treated with oxygen and a mixture of oxygen and tetrafluoroethylene in a cold plasma reactor for 30, 100 and 200 s. The single fibers were then tested in tensile mode and the mechanical strength was analyzed by using the Weibull distribution function.

Impedance matching for optimization of power transfer in a capacitively excited RF plasma reactor

In RF cold plasma reactors, energy transfer from the generator to the discharge is not perfect and only 50 to 70 percent (or even less) of the power is effectively transmitted to the discharge, the reMayning part being mostly dissipated in the matching network. The choice of this circuit is therefore the most important factor in view to optimize the energy transfer from the power supply to the plasma. Two classical networks, Π - and L -type, are analytically studied in their interaction with the experimental device. From this study, in both cases, numerical values are deduced for the coil inductance, and a capacitance range is determined for the capacitors. An experimental study in argon plasma at pressure range of 40-200 mTorr and at 13.56 MHz, performed with the two types of matching networks leads to a much effective energy transfer with the L -type, which must be chosen in order to improve the energetic yield of surface processing (sputtering or etching for instance) with a RF plasma reactor.

Effects of solution parameters on the deposition of YBa 2Cu 3O x phase prepared by aerosol feed method in a cold plasma reactor

Films of the superconducting phase YBa 2Cu 3O x (YBCO) were deposited by CVD using an aerosol feed technique in a cold plasma reactor. Aerosol droplets containing the three precursors were generated by an ultrasonic nebulizer operating at 1.63 MHz, while a 50 kW RF generator, operating at 2.87 MHz, was used to simultaneously create the plasma and heat a stainless steel susceptor. The YBCO films were deposited on single crystal MgO substrates at an oxygen partial pressure of 1.3 kPa, at a substrate temperature of 850 °C, using a deposition period of 30 min. Four different solution concentrations were used to study the effect of concentration on the microstructure of the films. The dried particle size was determined to have a significant effect on the microstructure, composition and deposition rate of the films.

Practical heat transfer model for oxygen‐fed ozone generators

Abstract Heat dissipation has a bad influence on ozone production reactor performance. In order to enhance our understanding of influence of operating parameters, a heat transfer model has been developed. Model predictions are in qualitative agreement with experimental results obtained on oxygen‐fed cold plasma reactors. Moreover, incidences of the local climate and of the cooling fluid temperature level on the ozone production cost are emphasized.

Optimal Ozone Production From Air

Abstract In this paper, another achieved example of Lunt's theory of chemical reactions in electrical discharges is emphasized. From an economic viewpoint, it is shown for a given mean value of the plasma temperature that the ozone yield of an air-fed cold plasma reactor presents an optimal value depending on the reduced electrical field, as expected from theoretical developments.

Modification of carbon surfaces in cold plasmas

Various forms of carbon, including carbon black, carbon fibre and pyrolytic graphite, have been surface-modified in a cold-plasma reactor. Plasma fluorination of the carbon surfaces was performed using variable flow rates, treatment times, and types of gas. The plasma-modified carbon surfaces were characterized using electron spectroscopy (ESCA), contact angle measurements, and scanning electron microscopy (SEM). The surface chemical structure of the plasma-fluorinated carbon blacks appeared to be similar to that of commercial Fluorographite. Nitrogen-containing groups were introduced into the surfaces of carbon blacks and carbon fibres by exposure to glow discharges in mixtures of ammonia and N2-H2. The surface concentration of functional groups containing nitrogen decreased with time. Several mechanisms for this degradation have been proposed. Plasma-modified carbon blacks and carbon fibres have potential for improving the properties of composites by achieving appropriate levels of adhesion between filler and matrix through physical compatibility and/or chemical bonding.

The Use of the Thermal and Electronic Effect in a Cold Plasma Reactor for Ozone Synthesis

Abstract Air or pure oxygen flowing into the discharge gap of a cold plasma reactor is the primary method for ozone production on commercial scale. The modelling of the conversion of oxygen into ozone has been set up by means of a kinetic scheme in which opposite reactions are considered. The forward reaction occurs via electronic activation, while the reverse reaction is temperature-dependent. Experimental results are in accord with this scheme, and lead to the following primary conclusions: the plasma temperature is a linear function of the applied power, while isothermal operation is the better from an economic point of view. The ozone molecule formed and destroyed in the cold plasma is suggested to be i.e., the first electronic excited state of ozone (triplet state).

Ozone Production: Economical Operation of a Cold Plasma Reactor

For a fixed value of the reduced electrical field, the economical operation of a cold plasma reactor generating ozone is determined by a particular value of the energy supplied by the field per molecule of reactant. Evidences are given in the ozone formation from air and oxygen. Moreover, influence of the flow and reduced electrical field upon the production is emphasized.